Ion implant process for defect elimination in metal layer planarization

ABSTRACT

The present disclosure describes a method for the planarization of ruthenium metal layers in conductive structures. The method includes forming a first conductive structure on a second conductive structure, where forming the first conductive structure includes forming openings in a dielectric layer disposed on the second conductive structure and depositing a ruthenium metal in the openings to overfill the openings. The formation of the first conductive structure includes doping the ruthenium metal and polishing the doped ruthenium metal to form the first conductive structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 63/002,291, titled “Ion Implant Process for DefectElimination in Metal Layer Planarization,” which was filed on Mar. 30,2020 and is incorporated herein by reference in its entirety.

BACKGROUND

Chemical mechanical polishing or planarization (CMP) is a process forsmoothing and planarizing surfaces with a combination of chemical andmechanical forces. CMP uses an abrasive chemical slurry in conjunctionwith a polishing pad and a retaining ring. In semiconductor fabrication,CMP is used to planarize and polish different types of materials (e.g.,dielectrics, metals, and semiconductors) having a crystalline,polycrystalline, or amorphous microstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures.

FIG. 1 is a cross-sectional view of metallization layer openings, inaccordance with some embodiments.

FIG. 2 is a flowchart of a method describing various operations for theformation of conductive structures in an interconnect layer, inaccordance with some embodiments.

FIGS. 3-8 are cross-sectional views of intermediate structures duringthe formation of conductive structures in an interconnect layer, inaccordance with some embodiments.

FIG. 9 is a cross-sectional view of a structure with conductivestructures thereon, in accordance with some embodiments.

FIG. 10 is a flowchart of a method describing various operations for theformation of conductive structures, in accordance with some embodiments.

FIGS. 11-15 are cross-sectional views of intermediate structures duringthe formation of conductive structures, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature on a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features are disposed between the first and second features,such that the first and second features are not in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition does not in itselfdictate a relationship between the various embodiments and/orconfigurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The term “nominal” as used herein refers to a desired, or target, valueof a characteristic or parameter for a component or a process operation,set during the design phase of a product or a process, together with arange of values above and/or below the desired value. The range ofvalues can be due to slight variations in manufacturing processes and/ortolerances.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, 2%, ±3%, ±4%, ±5% of the value). These values are merely examplesand are not intended to be limiting. It is to be understood that theterms “about” and “substantially” can refer to a percentage of thevalues as interpreted by those skilled in relevant art(s) in light ofthe teachings herein.

Ruthenium metal can be used as a fill material for conductive structuresin a middle-end-of-line (MEOL) process and a diffusion barrier/seedlayer for copper interconnects in a back-end-of-line (BEOL) process.This is because ruthenium metal exhibits low bulk resistivity (e.g.,about 7.7 μΩ·cm) and sufficient corrosion resistance to copper platingchemistries.

Integration of ruthenium in semiconductor manufacturing has itschallenges. For example, ruthenium, which is resistant to chemicalattack, is difficult to planarize (e.g., exhibits a low polishing rate)with existing chemical mechanical polishing (CMP) slurries like the onesused for other metals in semiconductor manufacturing like copper,aluminum, tungsten, cobalt, etc. Therefore, other CMP slurries aredeveloped for ruthenium planarization processes. These other CMPslurries require strong oxidizers-such as ceric ammonium nitrate((NH₄)₂Ce(NO₃)₆), sodium periodate (NaIO₄), potassium periodate (KIO₄),potassium permanganate (KMnO₄)—and long polishing times to removeruthenium metal layers. Long polishing times with strong oxidizers candamage surrounding materials. For example, strong oxidizers can causecopper galvanic corrosion—e.g., an electrochemical process in which onemetal (e.g., copper) corrodes preferentially when it is in electricalcontact with another metal (e.g., ruthenium) in the presence of anelectrolyte (e.g., the CMP slurry). In addition, the pH of the slurryemployed in ruthenium polishing needs to be controlled between about 8.4and about 10 to prevent the formation of ruthenium tetroxide (RuO₄),which is a toxic byproduct of the chemical reaction between theruthenium metal and the CMP slurry.

To address the aforementioned shortcomings, the embodiments describedherein are directed to an ion implant method configured to increase thepolishing rate of ruthenium metal for CMP slurries like the onesmentioned above and to reduce or minimize the ruthenium polishing time.Reduced ruthenium polishing times are beneficial for the surroundingmaterials as discussed above. In some embodiments, the implant methodincludes implants with an implant energy between about 0.3 keV and about50 keV and an incident angle between 0° and about 80°. In someembodiments, the dopant dose ranges between about 1×10¹⁴ dopants/cm² andabout 1×10¹⁷ dopants/cm² and includes dopants selected from a group ofcarbon (C), boron (B), phosphorous (P), oxygen (O), silicon (Si), argon(Ar), germanium (Ge), arsenic (As), xenon (Xe), or other suitabledopants. In some embodiments, after the implant process, the dopedruthenium layers are removed during a subsequent CMP process. Accordingto some embodiments, the polishing rate achieved for a doped rutheniumlayer is between about 1.1 and about 1.7 higher than that of an un-dopedruthenium layer. This is because dopants induce defects in the rutheniummetal. The doped ruthenium metal oxidizes faster during the rutheniumCMP process and therefore polishes faster. In some embodiments, implantprocess parameters that modulate the polishing rate of the rutheniumlayer during the CMP process include the dopant species, the dopantdose, the implant energy, and the incident angle at which the dopantsimpinge the surface of the ruthenium metal.

According to some embodiments, FIG. 1 is a partial cross-sectional viewof a partially fabricated interconnect layer 100 formed on a substrate110. At this fabrication stage, interconnect layer 100 includes openings120, 130, and 140 formed within a low-k dielectric 150 disposed onsubstrate 110. In subsequent operations, openings 120, 130, and 140 willbe filled with one or more conductive layers, including a rutheniumlayer, to form respective conductive structures for interconnect layer100. In some embodiments, FIG. 1 is a precursor structure (e.g., astarting structure) for the embodiments described herein.

By way of example and not limitation, substrate 110 can be a partiallyfabricated wafer with one or more layers formed thereon. These one ormore layers, which are not shown in FIG. 1 for simplicity, can include,for example, frond-end-line (FEOL) structures (e.g., active devices,passive devices, doped regions, epitaxial structures, etc.) and local orglobal interconnect layers (e.g., MEOL metallization layers, BEOLmetallization layers, or combinations thereof). Consequently,interconnect layer 100 can be a first BEOL layer of a stack of BEOLmetallization layers or any BEOL within a stack of BEOL metallizationlayers disposed on substrate 110. When formed, interconnect layer 100will be electrically coupled to underlying metallization layers (e.g.,MEOL and/or BEOL metallization layers) or devices of substrate 110. Forexample, conductive structures formed in openings 120 and 130 can be incontact with respective conductive structures of underlyingmetallization layers (e.g., MEOL or BEOL metallization layers) includedin substrate 110. The aforementioned layers and features included insubstrate 110, which are not shown in FIG. 1, are within the spirit andthe scope of this disclosure.

According to some embodiments, openings 120, 130, and 140 are formed bypatterning low-k dielectric 150—for example, by using sequentialphotolithography and etching operations. By way of example and notlimitation, openings 120 and 130 may require a double patterningprocess, while opening 140 may require a single patterning process. Insome embodiments, low-k dielectric 150 includes carbon-rich siliconoxide layer with or without pores having a dielectric constant betweenabout 2 and about 3. In some embodiments, low-k dielectric 150 includesa stack of dielectric layers, such as a low-k dielectric and anotherdielectric: (i) a low-k dielectric (e.g., carbon doped silicon oxide)and a silicon carbide with nitrogen doping; (ii) a low-k dielectric(e.g., carbon doped silicon oxide) and a silicon carbide with oxygendoping; (iii) a low-k dielectric (e.g., carbon doped silicon oxide) withsilicon nitride; or (iv) a low-k dielectric (e.g., carbon doped siliconoxide) with silicon oxide.

FIG. 2 is a flowchart of a method 200 describing various operations forthe formation of conductive structures in an interconnect layer, such asinterconnect layer 100 shown in FIG. 1. More specifically, method 200includes an implant process configured to improve the polishing rate ofruthenium metal layers deposited during the formation of conductivestructures in the interconnect layer. Other fabrication operations canbe performed between the various operations of method 200 and areomitted merely for clarity and ease of description. These variousoperations are within the spirit and the scope of this disclosure.Additionally, not all operations may be required to perform thedisclosure provided herein. Some of the operations may be performedconcurrently, or in a different order than the ones shown in FIG. 2. Insome embodiments, one or more other operations may be performed inaddition to or in place of the presently described operations. Method200 will be described in reference to FIGS. 1, 3-8.

In referring to FIG. 2, method 200 begins with operation 210 and theprocess of depositing a ruthenium metal liner in openings formed in adielectric layer of an interconnect layer. For example, the openings ofoperation 210 can correspond to openings 120, 130, and 140 formed inlow-k dielectric 150 of interconnect layer 100 shown in FIG. 1. By wayof example and not limitation, FIG. 3 shows interconnect layer 100 afteroperation 210 and the deposition of ruthenium metal liner 300 inopenings 120, 130, and 140. In some embodiments, ruthenium metal liner300 is blanket-deposited on interconnect layer 100 to cover exposedsurfaces of low-k dielectric 140 in areas inside and outside of openings120, 130, and 140 as shown in FIG. 3. In some embodiments, rutheniummetal liner 300 is deposited with a chemical vapor deposition (CVD)process or an atomic layer deposition (ALD) process at a temperaturebelow about 200° C. (e.g., about 180° C.) using a ruthenium carbonylprecursor chemistry, such as triruthenium dodecacarbonyl (Ru₃(CO)₁₂). Insome embodiments, ruthenium metal liner 300 is deposited at anappropriate thickness to serve as a barrier/seed layer for copper metal.For example, the thickness of ruthenium metal liner 300 can rangebetween about 3 Å and about 30 Å.

In referring to FIG. 2, method 200 continues with operation 220 and theprocess of depositing copper metal on the ruthenium metal liner (e.g.,ruthenium metal liner 300) to fill the openings (e.g., openings 120,130, and 140) of the interconnect layer (e.g., interconnect layer 100).In some embodiments, FIG. 4 shows interconnect layer 100 after operation220 where copper metal 400 is deposited on ruthenium metal liner 300 andsubstantially fills openings 120, 130, and 140 shown in FIG. 3. In someembodiments, copper metal 400 is grown by a suitable method (e.g., byelectroplating) directly on ruthenium metal liner 300. According to someembodiments, copper metal 400 extends over top surfaces of low-kdielectric 150 as shown in FIG. 4 and forms an overburden 410 which willbe subsequently removed (e.g., polished down) by a copper CMP process.

In referring to FIG. 2, method 200 continues with operation 230 and theprocess of polishing copper metal 410 with a copper CMP process. Inreferring to FIG. 4, copper CMP process 420 removes copper overburden410 according to operation 230. In some embodiments, copper CMP process420 is incapable of removing ruthenium metal liner 300 from top surfacesof low-k dielectric 150 for the reasons discussed above. For example,copper CMP process 420 polishes copper metal 400 at a higher rate thanruthenium metal liner 300. Therefore, after copper CMP process 420,ruthenium metal liner 300 appears “raised” with respect to top surfacesof copper metal 400 as shown in the resulting structure of FIG. 5. Insome embodiments, if copper CMP process 420 is allowed to continue in aneffort to remove ruthenium metal liner 300, copper CMP process 420 willcause excessive copper dishing—e.g., copper CMP process 420 will furtherrecess the top surface of copper metal 400 compared to the surroundingmaterials (e.g., ruthenium metal layer 300 and low-k dielectric 150).

In referring to FIG. 2, method 200 continues with operation 240 and theprocess of doping ruthenium metal liner 300 with an implant process. Insome embodiments, unlike an un-doped ruthenium metal liner, the dopedruthenium metal liner 300 can be easily oxidized and subsequentlyremoved (e.g., polished) from the top surface of low-k dielectric 150with a ruthenium CMP process. In some embodiments, the implant processinduces defects in the ruthenium metal, which accelerate the rutheniumoxidation rate during the CMP process.

During the implant process of operation 240, ionized dopants 600 areaccelerated towards substrate 110 and impinge the top surfaces ofinterconnect layer 100 at an incident angle θ as shown in FIG. 6. Insome embodiments, incident angle θ, which is measured from a directionnormal to substrate 110 (e.g., from the z-direction), ranges from about0° to about 80°. For example, ionized dopants 600A in FIG. 6 impinge thetop surface of interconnect layer 100 at a normal angle (e.g., at anincident angle θ equal to 0°) and ionized dopants 600B impinge the topsurface of interconnect layer 100 at an incident angle of about 45°. Insome embodiments, small incident angles (e.g., closer to 0°) allowionized dopants 600 to penetrate deeper into low-k dielectric 150 ascompared, for example, to ionized dopants impinging the top surface ofinterconnect layer at large incident angles (e.g., closer to 80°). Forexample, implant depth D1 for ionized dopants 600A can be greater thanimplant depth D2 for ionized dopants 600B shown in FIG. 6 (e.g., D1>D2)under identical implant conditions with respect to dopant species anddopant energy. In some embodiments, incident angle θ is fixed for theduration of the implant process in operation 240.

In some embodiments, the implant depth within low-k dielectric 150 canbe larger than that in ruthenium metal liner 300 and copper metal 410.This is because low-k dielectric 150 has a lower density compared toruthenium metal liner 300 and copper metal 410. For example, low-k 150can be porous. Further, the implant process of operation 240 may damagelow-k dielectric 150. In some embodiments, parameters of the implantprocess, like incident angle θ, can be used to control the implant depthand mitigate the damage induced to low-k dielectric 150 by the dopants.For example, a grazing incident angle θ (e.g., closer to about 80°) canbe used to reduce the implant depth in low-k dielectrics that aresusceptible to damage during the implant process of operation 240.

In addition to incident angle θ, the implant depth can be controlledthrough the implant energy of ionized dopants 600, which can range fromabout 0.3 keV to about 50 keV. In some embodiments, for a fixed incidentangle θ and identical dopant species, high implant energies (e.g.,closer to about 50 keV) can result in a larger implant depth compared tolow implant energies (e.g., closer to about 30 KeV). In someembodiments, the implant depth can be adjusted by incident angle θ, theimplant energy of the ionized dopants, or a combination thereof tomitigate the implant damage to low-k dielectric 150. This ensures thatruthenium metal liner 300 is removed during the ruthenium CMP processwithout compromising the underlying low-k dielectric 150.

In some embodiments, non-polished portions of ruthenium metal liner 300,copper metal 400, and low-k dielectric 150 may include a residual dopantconcentration equal to or greater than about 1×10¹² atoms/cm³. Forexample, a dopant concentration of about 1×10¹² atoms/cm³ or greater maybe detected with secondary ion mass spectroscopy (SIMS) in low-kdielectric 150 after the ruthenium CMP process. In some embodiments, theshaded top portion of ruthenium interconnect layer 100 shown in FIG. 6represents an exemplary doped region formed by the implant process ofoperation 240. In some embodiments, the doped region has a taildistribution towards its bottom surface, which can be detected in thenon-polished portions as discussed above. In other words, the bottomsurface of the doped region shown in FIG. 6 may not be sharp butincludes a tail with a residual dopant concentration equal to or greaterthan about 1×10¹² atoms/cm³.

In some embodiments, the implant process of operation 240 furtherincludes a dopant dose between about 1×10¹⁴ dopants/cm² and about 1×10¹⁷dopants/cm². In some embodiments, ionized dopants 600 include, but arenot limited to, C, B, P, O, Si, Ar, Ge, As, Xe, or any suitable dopant.In some embodiments, some dopant species may not be detectable withSIMS. For example, SIMS may be unable to determine the concentration ofO, Xe, or Ar in low-k dielectric 150. According to some embodiments, theionized dopants induce defects in ruthenium metal liner 300, whichaccelerate the oxidation of ruthenium metal liner 300 when rutheniummetal liner 300 is exposed to a ruthenium CMP slurry. In someembodiments, doped ruthenium metal oxidizes at a higher rate thanun-doped ruthenium metal. In some embodiments, the polishing rateachieved for a doped ruthenium metal liner is between about 1.1 andabout 1.7 times higher than that of an un-doped ruthenium metal liner.

In some embodiments, the CMP polishing rate for the ruthenium metalliner is modulated through implant process parameters, such as thedopant species used (e.g., the atomic mass of the dopant species), theimplant energy, the incident angle, and the dopant dose. Theaforementioned implant process parameters can control the defects or the“damage” induced to ruthenium metal liner 300 by the dopants, andtherefore the oxidation rate of ruthenium metal liner 300 during asubsequent CMP process.

In some embodiments, the process parameters for the implant processdescribed in operation 240 are selected as follows. Initially, thedopant species are selected. Based on the atomic mass of the dopantspecies, the implant energy and incident angle θ are selected to achievethe desired implant depth. Considerations for the implant depth include,but are not limited to, the material of low-k dielectric 150 and itstolerance to implant damage and the thickness of ruthenium liner 300 tobe polished. By way of example and not limitation, the implant energyand incident angle θ can be provided by an implant simulator softwarethat uses the atomic mass of the dopant species and the implant depth asinput parameters. Once the dopant species, the implant energy, and theincident angle θ are determined, the dopant dose is selected based onthe desired amount of dopants to be implanted in ruthenium liner 300.

In some embodiments, heavier dopants (e.g., with a higher atomic mass,like Xe and As) require a lower dopant dose compared to lighter dopants(e.g., with a lower atomic mass, like C and Ar) to achieve comparableruthenium polishing rates. In some embodiments, the implant depthachieved by heavier dopants can be different from the implant depthachieved by lighter dopants. In some embodiments, implant energies lessthan about 0.3 keV and dopant doses lower than about 1×10¹⁴ dopants/cm²do not substantially increase the polishing rate of ruthenium liner 300.On the other hand, implant energies greater than about 50 keV and dopantdoses higher than about 1×10¹⁷ dopants/cm² can damage low-k dielectric150.

In referring to FIG. 2, method 200 continues with operation 250 and theprocess of polishing the doped ruthenium metal liner 300 with aruthenium CMP process to form conductive structures in interconnectlayer 100. In referring to FIG. 7, ruthenium CMP process 700 planarizesand removes doped ruthenium metal liner 300 within an implant depth D(e.g., the top shaded portion of interconnect layer 100). In someembodiments, ruthenium CMP process 700 removes copper metal 400 andlow-k dielectric 150 at a substantially similar polishing rate withdoped ruthenium metal liner 300 to achieve a planarized top surfacetopography for interconnect layer 100 as shown in FIG. 8. In someembodiments, and in referring to FIGS. 7 and 8, height H1 ofinterconnect layer 100 prior to ruthenium CMP process 700 is greaterthan height H2 of interconnect layer 100 after ruthenium CMP process 700(e.g., H1>H2). By way of example and not limitation, the differencebetween heights H1 and H2 can be equal to, greater than, or less thanimplant depth D shown in FIG. 7.

According to some embodiments, after ruthenium CMP process 700, one ormore interconnect layers (not shown in FIG. 8) are formed oninterconnect layer 100. Method 200 can be repeated for any additionalinterconnect layer that includes a ruthenium metal liner and is formedon interconnect layer 100.

In some embodiments, the implant process of operation 240 in method 200is not limited to BEOL interconnect layers with ruthenium metal linerslike interconnect layer 100. For example, the implant process ofoperation 240 in method 200 can be used whenever planarization ofruthenium metal is required in the semiconductor fabrication process. Insome embodiments, the implant process of operation 240 can be used topolish/planarize MEOL liner-free conductive structures filled withruthenium metal, like line-free conductive structures 900 shown in FIG.9.

According to some embodiments, FIG. 9 is a cross-sectional view of astructure with conductive structures 900 formed on a cobalt conductivestructure 905. In some embodiments, conductive structures 900 are filledwith ruthenium metal 910. In some embodiments, conductive structures 900are liner-free or barrier-free conductive structures filled withruthenium metal 910. As shown in FIG. 9, cobalt conductive structure 905is formed on a merged source/drain epitaxial structure 915 grown on finstructures 920—which are in turn disposed on a substrate 925. In someembodiments, fin structures 920 and bottom portions of source/drainepitaxial layer 915 are surrounded by a first dielectric layer 930,while upper portions of source/drain epitaxial layer 915 and cobaltconductive structure 905 are surrounded by a second dielectric layer935. In some embodiments, first dielectric layer 930 forms an isolationstructure, such a shallow trench isolation (STI).

The top and mid-sections of conductive structures 900 (e.g., abovecobalt conductive structure 905) are surrounded by an etch stop layer940 and an interlayer dielectric (ILD) 945. In contrast, bottom sectionsof conductive structures 900 (e.g., below the top surface of cobaltconductive structure 905) are embedded in cobalt conductive structure905. The bottom sections of conductive structures 900 (e.g., withincobalt conductive structure 905) may or may not feature an “anchor” 950that prevents ruthenium metal 910 from being “pulled-out” during theruthenium planarization process (e.g., during the ruthenium CMPprocess). Anchor 950 also increases the surface area between rutheniummetal 910 and cobalt conductive structure 905 to reduce the contactresistance between the two structures. In some embodiments, a silicidelayer 955 is interposed between cobalt conductive structure 905 andsource/drain epitaxial structure 915 to reduce the electrical resistancebetween cobalt conductive structure 905 and source/drain epitaxialstructure 915.

The structures shown in FIG. 9 are exemplary and variations are withinthe spirit and the scope of this disclosure. For example, each finstructure 920 can have its own source/drain epitaxial structure insteadof a single merged source/drain epitaxial structure 915. Further,additional or fewer conductive structures 900 can be formed on cobaltconductive structure 905. Additional or fewer fin structures 920 canalso be formed on substrate 925. Further, FIG. 9 shows selectiveportions of the structures and other portions are not shown forsimplicity. For example, liner layers, barrier layers, or adhesionlayers for cobalt structure 905 are not shown in FIG. 9. Further, a gatestructure formed on fin structures 920 adjacent to source/drainepitaxial structure 915 along the x-direction, spacer structures, dopedregions, and capping layers for source/drain epitaxial structure 915 andfin structures 920 are not shown.

In some embodiments, cobalt structure 905 is a source/drain contact onwhich conductive structures 900 are formed without intervening layers,such as barrier layers, liner layers, or adhesion layers. In someembodiments, conductive structures 900 form a network of verticalcontacts that electrically connect cobalt structure 905 to upperinterconnect layers, such as interconnect layer 100 shown in FIG. 8.According to some embodiments, conductive structures 900 are polishedusing similar processes used in operations 240 and 250 of method 200shown in FIG. 2.

FIG. 10 is a flowchart of a method 1000, which describes operations forthe formation of conductive structures 900 in ILD 945 shown in FIG. 9.More specifically, method 1000, like method 200 shown in FIG. 2,includes an implant process configured to increase the polishing rate ofruthenium metal 910 deposited during the formation of conductivestructures 900. Other fabrication operations can be performed betweenthe various operations of method 1000 and are omitted merely for clarityand ease of description. These various operations are within the spiritand the scope of this disclosure. Additionally, not all operations maybe required to perform the disclosure provided herein. Some of theoperations may be performed concurrently, or in a different order thanthe ones shown in FIG. 10. In some embodiments, one or more otheroperations may be performed in addition to or in place of the presentlydescribed operations. Method 1000 will be described in reference toFIGS. 11-15.

In some embodiments, FIG. 11 is the structure shown in FIG. 9 prior tothe formation of conductive structures 900 and FIG. 12 is the structureshown in FIG. 11 after the formation of contact openings 1100 in ILD 945but prior to the deposition of ruthenium metal 910. By way of exampleand not limitation, contact openings 1100 in ILD 945 can be formed withsequential photolithography and etching operations. In some embodiments,FIG. 12 is a precursor structure (e.g., a starting structure) for method1000 shown in FIG. 10.

In the example of FIG. 12, contact openings 1100 are formed with an“anchor recess” 1110. However, this is not limiting and contact openings1100 can be formed without anchor recess 1110. In some embodiments,selective contact openings 1100 are formed with an anchor recess 1110.

In referring to FIG. 10, method 1000 begins with operation 1010 and theprocess of depositing ruthenium metal (e.g., ruthenium metal 910) incontact openings (e.g., contact openings 1100) formed in a dielectriclayer (e.g., ILD 945). By way of example and not limitation, rutheniummetal 910 can be deposited with similar methods used for the depositionof ruthenium metal liner layer 300. For example, ruthenium metal 910 canbe deposited with a CVD process, an ALD process or with anotherappropriate method at a temperature below about 200° C. (e.g., about180° C.) using a ruthenium carbonyl precursor chemistry, such asRu₃(CO)₁₂. In some embodiments, the ruthenium metal is deposited at athickness of about 20 nm or at a thickness sufficient to substantiallyfill openings 1100, including anchor recess 1110.

In some embodiments, FIG. 13 is a magnified view of contact openings1100 shown in FIG. 12 after the deposition of ruthenium metal 910according to operation 1010. In some embodiments, ruthenium metal 910fills the contact openings in ILD 945 and forms an overburden over topsurfaces of ILD 945 as shown in FIG. 13. The overburden will be removedby a ruthenium CMP process so that liner-free contacts 900 are formed.As discussed above, ruthenium metal 910 is deposited directly on cobaltstructure 905 without the presence of intervening layers. Further,ruthenium metal 910 is in direct contact with sidewall surfaces of etchstop layer 940 and ILD 945, which collectively form the sidewallssurfaces of opening 600 shown in FIG. 12.

In referring to FIG. 10, method 1000 continues with operation 1020 andthe process of doping ruthenium metal 910 with an implant process.According to some embodiments, operation 1020 of method 1000 is similarto operation 240 of method 200 shown in FIG. 2. For example, the implantprocess of operation 1020 and the implant process of operation 240 sharecommon operating principles. For example, during the implant process ofoperation 1020, ionized dopants 600 are accelerated towards substrate925 (e.g., shown in FIG. 12) and impinge top surfaces of ruthenium metal910 and ILD 945 at an incident angle θ shown in FIG. 13. In someembodiments, incident angle θ is measured from a direction normal to theplanar top surface of ILD 945 (e.g., from the z-direction). In someembodiments, incident angle θ ranges from about 0° to about 80°. Forexample, ionized dopants 600A in FIG. 13 impinge the top surface of ILD945 at a normal angle (e.g., an incident angle θ equal to 0°) andionized dopants 600B impinge the top surface of ILD 945 at an incidentangle of about 45°. In some embodiments, small incident angles (e.g.,closer to 0°) allow ionized dopants 600 to penetrate deeper intoruthenium metal 910 and ILD 945 as compared to ionized dopants withlarge incident angles (e.g., closer to 80°). For example, implant depthD3 of ionized dopants 600A is greater than implant depth D4 of ionizeddopants 600B (e.g., D3>D4) under similar implant conditions (e.g.,implant energy and dopant species). In some embodiments, incident angleθ is fixed for the duration of the implant process in operation 1020.

Similar to the implant process discussed above with respect operation240, in the implant process of operation 1020, the implant depth can becontrolled through the energy of ionized dopants 600. In someembodiments, the implant energy of the ionized dopants ranges betweenabout 0.3 keV and 50 keV. In some embodiments, for a fixed incidentangle θ and for the same type of dopants, high implant energies (e.g.,about 50 keV) can result in a larger implant depth compared to lowimplant energies (e.g., about 30 keV). In some embodiments, the implantdepth is adjusted by incident angle θ, the implant energy of the ionizeddopants, or a combination thereof.

In some embodiments, non-polished portions of ruthenium metal 910 andILD 945 may include a residual dopant concentration equal to or greaterthan about 1×10¹² atoms/cm³. For example, a dopant concentration ofabout 1×10¹² atoms/cm³ or greater may be detected with SIMS in ILD 945.In some embodiments, the shaded top portion of ruthenium metal 910 andILD 945 shown in FIG. 13 represents an exemplary doped region withinruthenium metal 910 and ILD 945 achieved by the implant process ofoperation 1020.

In some embodiments, the implant process of operation 1020 furtherincludes a dopant dose between about 1×10¹⁴ dopants/cm² and about 1×10¹⁷dopants/cm². In some embodiments, ionized dopants 600 include, but arenot limited to, C, B, P, O, Si, Ar, Ge, As, or Xe. According to someembodiments, the ionized dopants induce defects in ruthenium metal 910that accelerate the oxidation of ruthenium metal 910 when the latter isexposed to a ruthenium CMP slurry. In some embodiments, doped rutheniummetal has a higher polishing rate compared to un-doped ruthenium metalwhen both are polished under similar CMP processing conditions. In someembodiments, the polishing rate of doped ruthenium metal is betweenabout 1.1 and about 1.7 times higher than that of un-doped rutheniummetal.

As discussed above with respect to the implant process of operation 240,the CMP polishing rate for the ruthenium metal can be modulated througha combination of implant process parameters, such as the type of dopantspecies (e.g., the atomic mass of the dopant species), the implantenergy, the incident angle, and the dopant dose. The aforementionedimplant process parameters control the defects or the “damage” inducedto ruthenium metal 910 by the dopants, and therefore the oxidation rateof ruthenium metal 910 during a subsequent CMP process.

The process parameters for the implant process described in operation1020 can be selected as described in operation 240. For example, thedopant species can be selected first, followed by the implant energy andincident angle, followed by the implant dose.

In some embodiments, heavier dopants require a lower dopant dose thanlighter dopants to achieve comparable ruthenium polishing rates. In someembodiments, the implant depth achieved by heavier dopants is differentfrom the implant depth achieved by lighter dopants. In some embodiments,implant energies less than about 0.3 keV and dopant doses lower thanabout 1×10¹⁴ dopants/cm² do not substantially increase the polishingrate of ruthenium liner 300. On the other hand, implant energies greaterthan about 50 keV and dopant doses higher than about 1×10¹⁷ dopants/cm²can damage ILD 945.

In referring to FIG. 10, method 1000 continues with operation 1030 andthe process of polishing the doped ruthenium metal 910 with a rutheniumCMP process to form conductive structures (e.g., conductive structures900). In referring to FIG. 14, ruthenium CMP process 1400 planarizes andremoves doped ruthenium metal within an implant depth D and theruthenium metal overburden over ILD 945. In some embodiments, rutheniumCMP process 1400 removes the ruthenium metal and ILD 945 at asubstantially similar polishing rate to achieve a planarized top surfacetopography as shown in FIG. 15. In some embodiments, and in referring toFIG. 14, height H3 of ILD 945 prior to ruthenium CMP process 1400 islarger than height H4 of ILD 945 after ruthenium CMP process 1400 (e.g.,H3>H4). By way of example and not limitation, the difference between H3and H4 is substantially equal to implant depth D shown in FIG. 14.

In some embodiments, ruthenium CMP process 1400 is different from theruthenium CMP process 250 due to the differences between the polishedmaterials.

According to some embodiments, after ruthenium CMP process 1400, one ormore interconnect layers (e.g., like interconnect layer 100 shown inFIG. 8) can be formed on conductive structures 900 and ILD 945.

Various embodiments in accordance with this disclosure are directed to amethod for the planarization of ruthenium metal layers in MEOL and BEOLconductive structures. In some embodiments, the ruthenium metal isimplanted (doped) with dopant species to increase its polishing rateduring a subsequent ruthenium CMP process. In some embodiments, theimplant process includes implants with an implant energy between about0.3 keV and about 50 keV and an incident angle between 0° and about 80°.In some embodiments, the implant dose ranges between about 1×10¹⁴dopants/cm² and about 1×10¹⁷ dopants/cm² and includes dopants selectedfrom C, B, P, O, Si, Ar, Ge, As, or Xe. In some embodiments, the dopedruthenium layers are removed during a subsequent CMP process. In someembodiments, a residual dopant concentration of about 1×10¹³ atoms/cm³or greater may be detected with SIMS in the surrounding dielectricmaterial after the ruthenium CMP process. In some embodiments, dopedruthenium metal layers oxidize faster than un-doped ruthenium metallayers during a ruthenium CMP process. In some embodiments, dopedruthenium metal layers have a polishing rate that is between about 1.1and about 1.7 times the polishing rate of un-doped ruthenium metallayers.

In some embodiments, a method includes forming a first interconnectlayer on a substrate, where forming the first interconnect layerincludes forming openings in a dielectric layer disposed on thesubstrate, depositing a ruthenium metal liner in the openings, anddepositing copper metal on the ruthenium metal to fill the openings.Forming the first interconnect layer further includes polishing thecopper metal, doping the ruthenium metal liner, and polishing the dopedruthenium metal liner to form conductive structures in the firstinterconnect layer. The method further includes forming a secondinterconnect layer on the first interconnect layer.

In some embodiments, a method includes forming a first conductivestructure on a second conductive structure, where forming the firstconductive structure includes forming openings in a dielectric layerdisposed on the second conductive structure and depositing a rutheniummetal in the openings to overfill the openings. Forming the firstconductive structure further includes doping the ruthenium metal andpolishing the doped ruthenium metal to form the first conductivestructure. The method also includes forming an interconnect layer on thefirst conductive structure.

In some embodiments, an interconnect layer includes a dielectric layeron a substrate, conductive structures in the dielectric layer, where theconductive structures include a first conductive material and aruthenium liner surrounding sidewall and bottom surfaces of the firstconductive material. Further, the dielectric layer includes dopantshaving a dopant concentration of at least about 1×10¹³ atoms/cm³.

It is to be appreciated that the Detailed Description section, and notthe Abstract of the Disclosure, is intended to be used to interpret theclaims. The Abstract of the Disclosure section may set forth one or morebut not all exemplary embodiments contemplated and thus, are notintended to be limiting to the subjoined claims.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art will appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art will also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the subjoined claims.

What is claimed is:
 1. A method, comprising: forming a firstinterconnect layer on a substrate, wherein forming the firstinterconnect layer comprises: forming openings in a dielectric layerdisposed on the substrate; depositing a ruthenium metal liner in theopenings; depositing copper metal on the ruthenium metal liner to fillthe openings; polishing the copper metal, doping the ruthenium metalliner; and polishing the doped ruthenium metal liner to form conductivestructures in the first interconnect layer; and forming a secondinterconnect layer on the first interconnect layer.
 2. The method ofclaim 1, wherein depositing the ruthenium metal liner comprisesdepositing the ruthenium metal liner on surfaces of the dielectric layeroutside the openings.
 3. The method of claim 1, wherein doping theruthenium metal liner comprises doping a portion of the copper metal anda portion of the dielectric layer.
 4. The method of claim 1, whereinpolishing the doped ruthenium metal liner comprises polishing the coppermetal, the dielectric layer, and the doped ruthenium metal liner at asubstantially similar polishing rate.
 5. The method of claim 1, whereindoping the ruthenium metal liner comprises doping the ruthenium metalliner with carbon (C), boron (B), phosphorous (P), oxygen (O), silicon(Si), argon (Ar), germanium (Ge), arsenic (As), or xenon (Xe).
 6. Themethod of claim 1, wherein doping the ruthenium metal liner comprisesdoping the ruthenium metal liner with a doping process comprising an ionbeam with an incident angle between about 0° and about 80°.
 7. Themethod of claim 1, wherein doping the ruthenium metal liner comprisesdoping the ruthenium metal liner with a doping process comprisingdopants with an ion energy between about 0.3 keV and about 20 keV.
 8. Amethod, comprising: forming a first conductive structure on a secondconductive structure, wherein forming the first conductive structurecomprises: forming openings in a dielectric layer disposed on the secondconductive structure; depositing a ruthenium metal in the openings tooverfill the openings; doping the ruthenium metal; and polishing thedoped ruthenium metal to form the first conductive structure; andforming an interconnect layer on the first conductive structure.
 9. Themethod of claim 8, wherein doping the ruthenium metal comprises dopingtop portions of the ruthenium metal and top portions of the dielectriclayer with carbon (C), boron (B), phosphorous (P), oxygen (O), silicon(Si), argon (Ar), germanium (Ge), arsenic (As), or xenon (Xe).
 10. Themethod of claim 8, wherein doping the ruthenium metal comprises doping atop portion of the ruthenium metal to form a top doped portion and abottom non-doped portion.
 11. The method of claim 8, wherein doping theruthenium metal comprises exposing the ruthenium metal to a dopant dosebetween about 1×10¹⁴ dopants/cm² and about 1×10¹⁷ dopants/cm².
 12. Themethod of claim 8, wherein doping the ruthenium metal comprisesincreasing a polishing rate of the doped ruthenium metal by about 1.1 toabout 1.7 times.
 13. The method of claim 8, wherein doping the rutheniummetal comprises doping the ruthenium metal deposited on the dielectriclayer outside the openings.
 14. The method of claim 8, wherein dopingthe ruthenium metal comprises doping a top portion of the dielectriclayer.
 15. The method of claim 8, wherein depositing the ruthenium metalcomprises depositing the ruthenium metal on surfaces of the dielectriclayer outside the openings to form an overburden.
 16. The method ofclaim 8, wherein polishing the doped ruthenium metal comprises polishingthe doped ruthenium metal with a chemical mechanical planarizationprocess.
 17. An interconnect layer, comprising: a dielectric layer on asubstrate; conductive structures in the dielectric layer, wherein theconductive structures comprise: a first conductive material; and aruthenium liner surrounding sidewall and bottom surfaces of the firstconductive material, wherein top surfaces of the ruthenium liner and topsurfaces of the first conductive material are coplanar; and wherein thedielectric layer comprises dopants having a dopant concentration equalto or greater than about 1×10¹² atoms/cm³.
 18. The interconnect layer ofclaim 17, wherein the first conductive material comprises copper. 19.The interconnect layer of claim 17, wherein the first conductivematerial is different from the ruthenium liner.
 20. The interconnectlayer of claim 17, wherein the dopants comprise carbon (C), boron (B),phosphorous (P), oxygen (O), silicon (Si), argon (Ar), germanium (Ge),arsenic (As), or xenon (Xe).